Conventional helicopter Vertical Take-Off and Landing (VTOL) aircraft configurations are generally limited to fewer than 170 knots for flight speed but can lift large loads. Present tilt rotor VTOL aircraft configurations have an intermediate flight speed capability at 300 knots but less lift capability than a helicopter. A conventional lift fan VTOL aircraft has capability for high-speed flight at over 400 knots but with further reduced lift load capability. A lift fan VTOL also can be more survivable, but ordinarily has required a complex and expensive propulsion system. Thus, there exists a need for an engine for a VTOL aircraft that is low cost, enables a survivable aircraft, and provides the capability for high flight speeds of around 300 knots with a loiter speed capability of around 150 knots with stationary hover capability, as well.
U.S. Pat. No. 4,286,430 discloses a turbine engine with three spools: a low-pressure spool, an intermediate spool and a high-pressure spool. The high-pressure spool is mounted off axis, and typically transverse relative to the other spools. An intake scroll tube ducts the compressed air from the intermediate spool compressor to the high-pressure spool assembly while, similarly, an exhaust scroll tube ducts the exhaust from the high-pressure turbine assembly and to the intermediate pressure turbine assembly.